Hey Scotty,2005 BMW x5. About 2 weeks ago, started misfire after I pressed the acceleration pedal almost to the floor. Decided to change spark plugs, and all but Cylinder 6 had a little oil on it. Still misfired, checked the coils all seem ok. Computer scan said cylinder 1 misfire after. Checked the spark plugs and cylinder one and it was the only plug that was black. My Mechanic did a compression test, 20 PSI on cylinder 1. 2,3,4,5,6 all between 150-200 PSI. The question is, can a damaged/leaking Valve cover gasket cause misfire and low compression or should I assume something is wrong with the valves, pistons or rings and take the engine in for a rebuild?
can a damaged/leaking Valve cover gasket cause misfire and low compression
Of course not. (Though if it leaked oil all over a coil it might cause a misfire.) Given the compression reading on that cylinder you have a serious internal engine problem.
should I assume something is wrong with the valves, pistons or rings and take the engine in for a rebuild?
You can perform a leakdown test to find out where the compression is being lost. Given the age of the vehicle you are probably looking at engine replacement. Due to their complexity, a factory-rebuilt engine is preferable to a local shop attempting the rebuild. Either way the cost is likely to be higher than the value of a 20-year-old X5.
@chucktobias Thank you for the reply. I added sea foam motor treatment to the gas tanks, 2 times already, just to see what happens. in both times vehicle ran better for a little. could that be an indication of something?
I wouldn't doubt that after 20 years your fuel injectors needed cleaning. Of course Seafoam would have no effect on a compression problem. (Seafoam is not a product that Scotty recommends but it probably did clean crud from your injectors.)
@chucktobias LOL, thank you, i know Scotty calls it CRAP, but hey anything is worth a shot especially the condition of the engine. So even though it ran good both times for a little then jumped back to misfire, is there a reason to believe the misfire could be the result of another issue causing the low compression? Sorry owned vehicles before but not a mechanic, so any help would be greatly appreciated.
There is no way that engine is going to run properly with only 20 PSI in one cylinder. It won't be as bad as a small 4-cylinder engine losing a cylinder but it's never going to be right. No additive is going to fix a mechanical problem. There's no rational reason to even have that expectation.
I would do a leakdown test to find where it's losing compression. If you're lucky maybe it's something repairable in the cylinder head like a cracked valve. (I've actually experienced that.) However it would still cost big $$$$ to fix if you don't do the work yourself, and then something else expensive could break. Frankly given the information you've provided here I'd say you should be shopping for a replacement vehicle.
@chucktobias Gotcha, thanks for your help.